Digesting lignocellulosic material with sodium hydroxymethylsulfonate

ABSTRACT

IMPROVEMENT IN A PROCESS FOR MANUFACTURING HIGH YEILD PULP IN WHICH COOKING TREATMENT AND MECHANICAL DEFIBRATION FOR LINOCELLULOSIC MATERIAL ARE COMBINED, SAID COOKING TREATMENT BEING CARRIED OUT IN ALKALINE CONDITION EMPLOYING A SULFOMETHYLATION AGENT WHICH IS PRODUCED FROM ADMIXING SODIUM SULFITE AND/OR SODIUM BISULFITE, FORMALDEHYDE AND WATER, SAID MECHANICAL DEFIBRATION BEING CARRIED OUT EITHER BEFORE OR AFTER THE COOKING.

United States Patent 3,711,366 DIGESTING LIGNOCELLULOSIC MATERIAL WITHSODIUM HYDROXYMETIIYLSULFONATE Junzo Nakano, Yuichiro Sumi, and MakotoNagata, Tokyo, Japan, assignors to The Kokusaku Pulp Industry Co., Ltd.,Tokyo, Japan No Drawing. Continuation-impart of application Ser. No.657,526, Aug. 1, 1967. This application Sept. 22, 1970, Scr. No. 74,469

Claims priority, application Japan, Aug. 3, 1966, 41/50,503

Int. Cl. D21b 1/16 US. Cl. 162-24 5 Claims ABSTRACT OF THE DISCLOSUREImprovement in a process for manufacturing high yield pulp in whichcooking treatment and mechanical defibration for lignocellulosicmaterial are combined, said cooking treatment being carried out inalkaline condition employing a sulfomethylation agent which is producedfrom admixing sodium sulfite and/or sodium bisulfite, formaldehyde andwater, said mechanical defibration being carried out either before orafter the cooking.

This application is a continuation-in-part of the copending Ser. No.657,526, filed on Aug. 1, 1967, now abandoned.

Various processes for producing high yield pulp have been suggested.High yield pulp has already been obtained by groundwood, chemigroundwoodand semichemical pulping processes but the high yield pulp so producedcontains more lignin than the conventional chemical pulp and, therefore,beating and refining have little effect, no or less fibrillationresults, and the strength of the paper produced therefrom is relativelylow. Thus, a process for making high yield pulp which is easily beatenand refined to produce a high strength paper is desired.

A sulfite process for red pine native to Japan employing formaldehyde asadditive was disclosed in the Journal of the Chemical Society of Japan,Industrial Chemistry Section 54, 195 and 397, 151 and 56, 277. Phenoliccompounds in the raw material reacted with the formaldehyde in thesulfite cooking liquor and condensation reaction, which was consideredto cause burnt cook, between. the phenolic compounds and lignin wasavoided. This process was useful for cooking red pine chips containingheart wood. E. Adler and L. Stockman disclosed in the SvenskPapperstidning 54, 477 that wood was subjected to chemical pulpingprocess using sulfite cooking liquor containing formaldehyde where burntcook was observed and it was considered that pulping is impossible.

Sodium sulfite or sodium bisulfite, formaldehyde and water are reactedto obtain sodium hydroxymethylsulfonate by the following reactions:

In the case of Reaction 1, it is recognized that about by weight of theoriginal sodium sulfite is converted into sodium hydroxymethylsulfonateunder the conditions described hereinafter in the examples; theresulting aqueous solution has a pH range of about 12.4 and 12.7. Theaqueous solution contains sodium sulfite, formaldehyde, sodiumhydroxymethylsulfonate and sodium hydroxide.

In Reaction 2, the sodium bisulfite is quantitatively converted intosodium hydroxymethylsulfonate and the resulting solution shows a pH ofabout 4.5. An alkali should be added to maintain the pH value in nearneutral to alkaline condition, i.e. at a pH from 5.7 to 13.7.

"ice

In the case of Reactionl, some of the Na SO added is converted into HOCHSO Na and the remaining is maintained in its original state, and, in thecase of Reaction 2, all of the Nal-ISO added isconverted into HOCH SO Naif Na SO NaHSO HCI-IO are employed, the following reaction would occur:

Thus, the composition of the liquid formed is complicated and it isdifiicult to analyze the composition by a conventional method. It is,however, possible to measure the pH value from which the amount ofNaOzl-I may be interpreted. Thus, the equilibrium values of theconstituents can be estimated from the degree of formation of NaOH. Itis necessary to adjust the pH value of the liquid to the rangeabovementioned.

The sulfomethylation agent produced as above reacts with lignin. Detailsof the reaction have not been confirmed, but it seems that:

(1) addition reaction of formaldehyde and the aromatic ring in ligninoccurs to form an alcoholic hydroxy group; subsequently the hydroxygroup is sulfonated with sodium sulfite or bisulfite to formsulfomethylated lignin;

(2) ortho position to phenolic hydroxy group in lignin is directlysulfomethylated with sodium hydroxymethylsulfonate; and

(3) in addition to the above, the side chain portion in lignin may alsobe sulfomethylated.

Lignocellulosic materials including soft and hard wood, straw, bamboo,grass and like are cooked by the aqueous solution when the lignin issulfomethylated according to the above reactions. Of course,side-reactions occur, for example, between other chemicals such assodium sulfite, sodium bisulfite and sodium hydroxide and non-cellulosicmaterials such as lignin, hemicellulose and others.

In cooking, that part of the lignin which does not com,- bine withcarbohydrates is dissolved in the cooking liquor, While the lignin thatcombines with the carbohydrates is not dissolved but is converted into ahydrophilic and soft state by sulfomethylation. The resulting cookedmaterial is easily defibrated mechanically without fiber shortening andspecific fiber damage. 7

Pulp so treated contains a larger amount'of lignin than the conventionalchemical pulps, so the yield of pulp according tothis invention is high.Furthermore, since the lignin is in a hydrophilic and soft state, fibercontaining such lignin is easily fibrillated by beating and refining.

Alternatively, lignocellulosic material predefibrated by, for example,grinder and refiner can then be cooked with the aqueous sulfomethylationagent solution.

Oneway of carrying out the present invention is to carry out the cookingunder elevated pressure and temperature employing a large amount of theaqueous sulfomethylation agent solution; this is similar to liquid phasecooking process. Another way is to immerse the lignocellulosic materialin the cooking liquor, then remove excess liquor, and subsequently, heatthe lignocellulosic material by steam as in the conventional vapor phasecooking process. In this case, the cooking time and liquid ratio wouldbe decreased.

The cooking conditions employed in this invention are a temperature ofabout C. to C., a pressure of about 0.5 kg./cm. gauge to 16 kg./cm.gauge, and the molar ratio of formaldehyde to sulfite and/or bisulfiteof 0.8 to 1.2, and, in the liquid phase cooking, a time of 20 minutes to5 hours, a liquid ratio of 2 to 20, preferably 3.5 to 8 and aconcentration of cooking liquor of about 5.to 30% by weight calculatedas S0 for lignocellulosic Liquid ratio the volume of the liquor added+Water in the wood chip (1.) the oven-dried weight of wood chip (kg)When lignocellulosic material is processed according to this inventionthepH value of the cooking liquor decreases as the reaction-proceeds,because an acid is produced from the lignocellulosic material and sodiumhydroxide is consurned by thereaction. However, it is desirable to bringthe pH value of the cooking liquor to a pH of-10.9 to l3.7, moresuitably 1'1. 9 to 12.7 when cooking treatment is started, and the endpointwill befrom 10.6 to 5.7, more suitably 9.6 to 6.7. Therefore, analkali should be added to the cooking liquor produced from sodiumbisulfite and formaldehyde to bring the pH within the range mentionedabove. In any case, care should be taken throughout the cookingtreatment to avoid an extremely acid condition.

The pulp produced in accordance with this invention has a brightness of47% to 53% and a light yellow colour. It is useful as unbleached pulp,but, if desired, it can be bleached 'with hydrogen peroxide to increasebrightness to about 70% Preferred embodiments of the present inventionwill be given by way of examples 'in which the novel process issuccessfullycarried out.

EXAMPLE 1 material was immersed in the solution and the excesssolutionwas removed at which'the pH value of the solution was 8.1". Theimmersed material was vapor phase cooked at a temperature of 148 C.under a pressure of 4.5 'kg./ cm. gauge for 8 minutes under theconditions of a liquid ratio of 1.6 anda S0 concentration of 4.1%, andthen defibratedfor 2 minutes at the sametemperature. The pH value ofth'e' cooking solution after defibration was 3.5. The yield-of pulpafter defibration was 89.8%. The pulp so obtained had a freeness of 780cc. (CSE) and'even after treatment with a La'mpenmill for 5 hours thefreeness was 770cc. '(CSF); The' decrease in freeness was extremelysmall. This was similar .to pulp produced by the Asplund'process inwhich lignocellulosic material was immersed in cooking liquor containing51.5 g. of sodium sulfite per liter, after removing the excess liquorheated at temperature of 148C. for one hour by steam and defibrated atthat temperature. Both pulps were unsatisfactory for use of paper.Furthermore, wood chips were processed with a similar aqueoussulfomethylation agent solution having pHvalue of 5.0; the pH valueafter the cooking reached 2.2. The resulting pulp had a dark browncolour, so that it could not be employed for paper industry. Thesephenomena support the idea that an extreme acid condition throughoutcooking treatment should be avoided.

' EXAMPLE 2 Mixed chips of six kinds of hard wood native. to Hokkaido,Japan, weighing 375 g. (oven dried weight was 300 g.) were evacuated.2325 ml. of cooking liquor containing 51.6 g. of SQdiurn sulfite and11.3 got formaldehyde 4 per liter (the molar ratio of formaldehyde tosulfite being 0.9, a liquidratio being 8.0 and a S0 concentration being20.3%) and having a pH of 12.7 was added to the chips. Cooking treatmentwas carried out at a temperature of 150 C. under a pressure of 5 kg./cm.gauge for 30 minutes. The pH value at end of the cooking was 7.9. Thecooked chips were separated from the cooking liquor and defibrated in aBauer laboratory disk refiner and the'knots were removed therefrom. Thepulp so obtained was treated by a Lampen mill and thenprepared intohandsheets having basis weight of 63 g./m. by TAPPI standard.

For comparative purposes the same procedure as above was carriedout,.except that the cooking liquor contained onlysodium sulfite.Characteristics of the pulps and strength of the handsheets are given inTable 1.

TABLE 1 Present invention Control Yield of pulp after defibration,percent 84. 7 85.3 Beating time (hours and minutes) 1. 05 1.05 Freeness(OSF cc.) 2-05 1105 Brightness, percent 44. 2 43. 2 Breaking length (k6. 1 4. 5 Burst factor 3. 5 2. 3 Tear factor 55 49- MIT foldingendurance 35 8 EXAMPLE 3 375 g. of chips and cooking liquor (the molarratio of formaldehyde to sulfite being 0.9), the same .as in Example 2,were employed. The evacuated chips were immersed in the cooking liquoruntil they had absorbed 480 to 500 ml. of the cooking liquor. The chipsso treated were charged into a laboratory defibrator and vapor phasecooked at 148 C. under a pressure of 4.5 kg./cm. gauge for 4 minutesunder the conditions of a liquid ratio of 1.6 and a S0 concentration of4.1%, and subsequently'defibrated at the same temperature for 2 minutes.The pH value of the cooking liquor aftertdefibration was 9.6. Y

The same kind of chips werevapor phase cooked and defibrated under thesame conditions as in the above procedure except that the aqueoussolution contained 171 g./l. of sodium sulfite and the cooking time was60 minutes. 1

Handsheets were prepared as described in Example 2 from both pulps.

Thecharacteristics of the pulps and handsh'eets are EXAMPLE 4 Sprucechips were defibrated by disc refiner and the fine portion was removed,g. of resulting fibers (oven dried weight being 88.7,. g.) was added to1000 ml. of aqueous solution containing 50 g. of sodium sulfite and 11g. of formaldehyde (the molar ratio of formaldehyde to sulfite being0.9, a liquid ratio being 11.4 and a S0 concentration being 27.7%).Cooking was carried'out' at a temperature of 150 C. under a pressure of5 log/cm. gauge for 2 hours. The pulp thus obtained was beaten in Lampenmill and prepared into haudsheets. The results are shown in Table 3.

EXAMPLE 5 The procedures described in Example 4 were followed but thecooking temperature and pressure were changed to 110 C. and 1 kg./cm.gauge. The results are shown in Table 4.

TABLE 4 Pulp yield, percent 95. 9 95. 9 Beating time (hours andminutes) 1. 2.00 Freeness (CSF cc.) E50 220 Breaking length (km.).. 3. 94. 6 Burst factor 1. 5 2. 2 Tear factor 36 2.9 MIT folding enduran 4 9EXAMPLE 6 375 g. of the same chips as in Example 2 were added to 2325ml. of cooking liquors, one of which contained 21.3 g. of sodiumbisulfite, 25.8 g. of sodium sulfite and 11.3 g. of formaldehyde perliter and had a pH value of 11.9 (Batch I) and another of whichcontained 51.6 g. of sodium sulfite and 11.3 g. of formaldehyde and hada pH value of 12.7 (Batch II). The molar ratio of formaldehyde tobisulfite and sulfite (Batch I) or sulfite (Batch II) was 0.9.

The pH values of the liquors after immersing of the chips were 11.1(Batch I) and 12.0 (Batch II).

The cooking treatment conditions were the same for Batches I and II- atemperature of 150 C. under a pressure of 5 kg./cm. gauge for two hoursunder the conditions of a liquid ratio of 8.0 and a S0 concentration of20.3%. The pH values at the end of the cooking were 6.7 (Batch I) and7.7 (Batch II).

On the other hand, for the purpose of comparison, the proceduresdescribed above were followed but the cooking liquor contained 42.6 g.of sodium bisulfite and 11.3 g. of formaldehyde and had a pH value of4.6 (Batch III). The pH value of the liquor after immersing of the chipswas 4.6. The pH value at the end of the cooking was 3.5.

The chips separated from the cooking liquor were defibrated in a Bauerlaboratory disk refiner and knots were removed therefrom. The pulps soobtained from Batches I, II and III were treated by a Lampen mill andthen prepared into handsheets having a basis weight of 63 g./m. by TAPPIstandard.

The characteristic of pulps and the strength of handsheets are given inTable 5.

TABLE 5 Batch I II III pH of cooking liquor 11. 9 12. 7 4. 6 Yield ofpulp after defibration, percent 80. 8 79. 8 79. 5 Beating time (min) byLampen 111111.. 45 36 P5 Freeness (C SF cc.) 315 310 325 Brightness,percent 47. 3 48. 5 31. 0 Breaking length (km. 5. 6 5. 9 2. 8 Burstfactor 3. 3 3. 9 1. 2 Tear factor 58 66 52 MIT folding endurance 33 52 2These results show that it is desirable to maintain the pH value ofcooking liquor in near neutral to alkaline condition during cooking.

EXAMPLE 7 Spruce chips weighing 375 g. (oven dried weight being 300 g.)were evacuated. 1725 ml. of cooking liquor containing 50 g. of sodiumsulfite and 11.9 g. of formaldehyde per liter (the molar ratio offormaldehyde to sulfite being 1.0) and having a pH of 12.7 was added tothe chips. Cooking treatment was carried out at a temperature of C.under a pressure of 5.7 kg./cm. gauge for 40 minutes under theconditions of a liquid ratio of 6.0 and a S0 concentration of 14.9%. ThepH value at end of the cooking was 7.7. The cooked chips were separatedfrom the cooking liquor and defibrated in a Bauer laboratory diskrefiner. The resulting pulp was beaten and prepared into handsheet asdescribed in Example 2.

The results are given in Table 6.

EXAMPLE 8 Spruce chips weighing 375 g. (oven dried weight being 300 g.)were evacuated. 1725 ml. of cooking liquor containing 30 g. ofsodiumsulfite and 5.7 g. of formaldehyde per liter (the molar ratio offormaldehyde to sulfite being 0.8) and having a pH of 12.5 was added tothe chips (Batch IV). Cooking treatment was carried out at a temperatureof C. under a pressure of 7.5 kg./cm. gauge for 80 minutes under theconditions of a liquid ratio of 6.0 and a S0 concentration of 9.0%. ThepH value at end of the cooking was 7.1.

The procedures described above were followed but the cooking liquorscontained 30 g. of sodium sulfite and 7.2 g. of formaldehyde (the molarratio of formaldehyde to sulfite being 1.0) (Batch V), and 30 g. ofsodium sulfite and 8.6 g. of formaldehyde (the molar ratio offormaldehyde to sulfite being 1.2) (Batch VI). In Batches V and VI, thepH values of the liquor before immersing of the chips and at the end ofthe cooking were 12.6 and 7.2, respectively.

The cooked chips were separated from the cooking liquor and defibratedin a Bauer laboratory disk refiner. The resulting pulps were beaten andprepared into handsheets as described in Example 2.

The results are given in Table 7.

What is claimed is: 1. A process of making high yield pulp, said processcomprising in combination:

(A) cooking treatment of lignocellulosic material, and (B) mechanicallydefibrating lignocellullosic material, (1) said cooking treatment beingcarried out in an aqueous cooking liquor by means of sodiumhydroxymethylsulfonate at a temperature of 100 C. to C. for a period oftime from a few minutes to 5 hours, at a liquid ratio of 1.0 to 20;

(i) said cooking liquor containing active pulping chemicals consistingessentially of an admixture selected from the group consisting of:

(a) sodium sulfite and formaldehyde;

(b) sodium bisulfite and formaldehyde;

and

(0) sodium sulfite, sodium bisulfite and formaldehyde;

the molar ratio of formaldehyde to sulfite, bisulfite, or sulfite .plusbisulfite being 1:08 to 1.2; (ii) said cooking liquor having a pH of10.9 to 13.7 at the start of cooking, and a chemical concentration of230% by weight calculated as S for lignocellulosic material, and aconcentration of formaldehyde of 0.7- 17% by weight; (2) saidmechanically defibrating being by means of a single disc refiner; and

(C) recovering high yield pulp.

2. A process of making pulp according to claim 1, wherein the cookingtreatment is carried out in liquid phase at a temperature within therange of 100 l90 C. for a time from twenty minutes to 5 hours, at aliquid ratio of 2 to 20 and in chemical concentration of 530% by weightas S0; for lignocellulosic materials.

3 A process of making pulp according to claim 1, wherein the cookingtreatment is carried out invapor phase at a temperature within the rangeof 100-l90 C., for a time from a few minutes to one hour, at a liquidratio of 1.0 to 4.0 and in concentration of 2 to 15% by.

weight calculated as S0 for lignocellulosic material.

4. A process of making pulp according to claim 1, wherein cookingtreatment and then mechanical defibration are carried out.

5. A process of making pulp according to claim 1, wherein mechanicaldefibration and then cooking treatment are carried out.

References Cited S. LEON BASHORE, Primary Examiner A. L. CORBIN,Assistant Examiner US. Cl. X.R. 16228, 72, 84

